The present invention relates to a channel selection apparatus employed in a television receiver (TV) or a video cassette recorder (VCR), and more particularly to a channel selection apparatus that automatically receives all the broadcast signals available in a given local area while identifying their station names. The channel selection apparatus then sorts the signals in a given order, and has tuning buttons to store the signals in the given order.
FIG. 3 is a block diagram illustrating a sorting technique of a channel selection apparatus already commercialized and employed in TVs and VCRs. The channel selection apparatus comprises the following elements:
(a) tuning section 31 for selecting a broadcast signal from antenna
(b) tuning voltage generator 32 for supplying a tuning voltage to tuning section 31 in order to receive a desired channel;
(c) broadcast signal detector 37 for determining availability of broadcast signals on a tuned frequency;
(d) text signal detector 33 for detecting text signals for identifying a broadcasting station associated with the broadcast signal detected by signal detector 37;
(e) error detector 35 for counting within a given time the number of parity errors of specified data from text signals of the broadcast signals received by tuning section 31;
(f) memory 34 for storing the frequencies of broadcast signals received by tuning section 31 and the names of broadcasting stations identified by detector 33;
(g) sorter 36 for (1) re-tuning the station stored in memory 34, the station having different frequencies, then (2) arranging the broadcast signals in the order of fewer parity errors based on the data supplied from error detector 35, and (3) assigning the arranged signals to the tuning buttons in the order of easier selecting operation.
The construction discussed above allows the channel selection apparatus to assign the frequencies of broadcasting stations of each state or each local area in a specified order to the tuning buttons of TVs or VCRs and to store these stations in the buttons. In other words, if a station has a plurality of on-air frequencies, the arrangement of stored frequencies can be changed so that the frequency containing fewer parity errors can be stored to the tuning button for easier selection. When the field intensities of both the broadcast signals to be compared are strong enough, a visual check can hardly distinguish the picture quality of both the signals. It is therefore possible to assign the broadcast signal having a text signal with a higher parity error rate to a tuning button for easier selection. The foregoing structure can avoid the problem discussed above.
When receiving a broadcast signal with a field intensity having sufficient strength, this structure, however, is rarely subjected to parity errors. The correlation between field intensity and parity-error-rate, however, is not always constant. In other words, correlation among picture quality by visual inspection, parity-error-rate and field intensity is not always constant in a practical use because of the following reason. Since both of the broadcast signals are subject to few errors in a steady state, an error in a non-steady state, such as a burst error due to noise disturbance, could influence both of the signals. Therefore, sorting a plurality of broadcast signals transmitted from the same station by a visual check does not always arrange the signals with fewer parity errors in the order of easier selecting operation.
Further, German Patent No. DE195 18 368 C1 discloses the following technique about determining the strength of a television signal based on a quality of a received teletext-signal out of broadcast signals. In order to evaluate strength of received broadcast signals including teletext information, a non-time-varied part is selected from the teletext signals, and this part is compared over a plurality of times. The broadcast signals are evaluated based on a number of different points of the comparison results. This German patent still has the same problem as discussed previously, i.e. since few errors are expected in a steady state under a practical field intensity, the comparison result is not always correct.
The present invention addresses the problem discussed above, and aims to provide a channel selection apparatus that can provide reliable sorting. A channel selection apparatus of the present invention includes the following steps to store a broadcast signal having the fewest parity errors by priority in a tuning button for an easier selecting operation. First, store in pairs into a memory all the names of the broadcasting stations and the corresponding frequencies available in the area where the channel selection apparatus is operated. Second, detect the broadcast signals having different frequencies under the same station name from the memory. Individually receive the detected plural broadcast signals with RF frequencies that are shifted from the normal frequency by a predetermined value so that the field intensity thereof is intentionally lowered. Then, detect only text data from the received broadcast signals, and compare it with a state of high error rate. Calculate the parity error rate of specified data from the respective text data, and compare the parity error rates of the plural broadcast signals. Finally, store the broadcast signal having the lowest parity error rate with priority in a tuning button of an easier selecting operation. Repeat the foregoing procedure until all the stations that have a plurality of RF frequencies for each broadcast signal undergo the procedure.
The operation described above can be automated, or manually activated according to the desires of a user.
As such, the strength of receiving-field-intensity correlates more closely with the parity-error-rate. As a result, frequencies stored in the tuning buttons are re-sorted so that the frequency having the strongest field intensity and producing the best picture quality is assigned to and stored in the tuning buttons of easiest selecting operation.